HONG KONG (Reuters) - Macquarie Group (>> Macquarie Group Limited), U.S.-based Principal Financial Group (>> Principal Financial Group Inc) and Singapore's United Overseas Bank (>> United Overseas Bank) are among suitors that have submitted bids for ING's (>> ING GROEP) Asian asset management business in a deal that may be worth around $500 million to $600 million, said sources familiar with the matter.

ING is selling its Asian asset management and insurance businesses in a roughly $7 billion deal to help repay the state bailout it received after the largest Dutch financial services company almost collapsed during the 2008 global crisis.

Japan's Nikko Asset Management and South Korea's Hanwha Group, which runs the life insurance unit of Korea Life Insurance Group (>> KOREA LIFE INSURANCE), have also placed bids in the first round of the sale that closed on Monday, said the sources, who declined to be identified as the process is confidential.

Ameriprise Financial Inc (>> Ameriprise Financial, Inc.), two Japanese financial institutions and Royal Bank of Canada (>> Royal Bank Of Canada) were also expected to have submitted indicative bids, one of the sources said.

Credit Suisse (>> Credit Suisse Group AG) is advising ING on the sale. Both companies declined to comment.

UOB, Principal, Macquarie, Hanwha and Ameriprise declined to comment, while Nikko and RBC could not be immediately reached for comment.

ING has dispatched information on the sale to more than 20 parties, underscoring the strong interest in the auction, though some potential suitors dropped out after studying the limited financial details in the sale documents, sources said.

U.S. fund manager BlackRock Inc (>> BlackRock, Inc.) was among the potential suitors, but it was unclear if the company submitted initial bids, according to the sources.

ING manages about 43.3 billion euros ($56.1 billion) of assets in the Asia-Pacific region, according to the latest company filing. It operates in Japan, South Korea, Taiwan, China, Hong Kong, Malaysia and Thailand, and employs about 230 investment professionals.

In China, Asia's No.2 asset management market behind Japan, ING has a joint venture with China Merchants Bank (>> China Merchants Bank Co., Ltd), in which the Dutch company owns a 33 percent stake.

DEBT FUNDS

Some potential suitors were disappointed to find that ING's product mix had more debt funds than equity, hedge funds and other alternative asset funds, one source familiar with the matter said.

Debt products earn relatively lower management fees than equity funds.

"The initial enthusiasm has cooled off. Some people didn't like what they saw under the bonnet," the source said.

ING's high cost base at its Asian headquarters of Hong Kong was cited as another reason that put off some potential buyers, sources said.

ING's does not give a breakdown of its Asian assets under management, but globally, only 23 percent of its 327.2 billion euros of assets is equity.

Profit from ING's global investment management business stayed flat at 45 million euros in the first quarter from a year ago, and was down from 53 million euros in the last quarter. ING does not give earnings details of its Asian investment management operations.

Asia's asset management industry, excluding Japan, is expected to double its assets to $4 trillion by 2015, driven by growing wealth in the region, rising foreign demand and new pools of assets from insurance and retirement funds, according to a report commissioned by Citigroup's (>> Citigroup Inc.) Securities and Fund Services.

(Reporting by Denny Thomas; Additional reporting by Narayanan Somasundaram, Saeed Azhar, Aaron Pressman, Miyoung Kim, Taiga Uranaka; Editing by Michael Flaherty and Ryan Woo)

By Denny Thomas